1. Field of the Invention
The present invention relates to a master carrier for magnetic transfer, which has a transfer-recording pattern arrayed in the track direction thereof in accordance with the information to be transferred to a magnetic recording medium, to an inspection method for it, and to a method for producing magnetic recording media by the use of it.
2. Description of the Related Art
Hard discs and high-density flexible discs that are desired to satisfy the requirements of mass storage and rapid access are supported by a tracking servo technique by which a magnetic head accurately scans and traces a narrow track width to reproduce signals at a high S/N ratio. According to the tracking servo technique, tracking servo signals, address information signals, regeneration clock signals and others are preformatted at predetermined intervals in one circle of every disc.
A magnetic head reads the preformatted signals on a disc and corrects its own position, and therefore it can accurately run along a predetermined track on the disc. Heretofore, discs are preformatted one by one or for every one track by the use of a dedicated servo-write device. However, such a servo-write device is expensive, and it takes a long period of time to preformat discs with it. Therefore, the servo-writing step accounts for the major part of the production costs of preformatted discs, and it is desired to reduce the costs thereof.
In that situation, a magnetic transfer method has been proposed in place of the method of preformatting one by one track on every disc, and it comprises transferring the necessary magnetic information all at a time. Precisely, the magnetic transfer method comprises keeping the surface of a magnetic recording medium (slave medium) that has a magnetic recording region in its surface, in intimate contact with the surface of a master carrier that has an uneven pattern on the surface of a support having a magnetic material in accordance with transfer information, and applying a transfer magnetic field to these in that condition to thereby transfer the magnetic pattern that corresponds to the information (servo signal) carried by the master carrier, into the magnetic recording region of the slave medium. The magnetic transfer method attains the necessary recording not requiring a relative position change of the master carrier and the slave medium, and it enables accurate preformatting of discs within an extremely short period of time. As a background of the invention, there is a reference of U.S. Pat. No. 6,347,016.
However, in order to improve the transfer quality in the above-mentioned magnetic transfer method, there is an important problem of how to keep the master carrier and the slave medium in intimate contact with each other with no clearance gap therebetween. This is because, if the two aren't kept enough in contact with each other therebetween, then a satisfactory recording signal intensity cannot be obtained and the intended magnetic transfer may not be attained in some region. The magnetic transfer failure causes signal drop of the magnetic information transferred to the slave medium, and the transferred signal quality is thereby lowered, and when the recorded signal is a servo signal, then it could not satisfactorily attain its tracking function and the signal-reading reliability thereof may therefore lower. To that effect, uniform signal recording in all over the disc area is important in the art of magnetic transfer.
We carried out a magnetic transfer test of recording a large number of slave medium sheets from one and the same master carrier, and inspected the signals recorded on the slave medium sheets. As a result, we found that signal drop occurred in the region of an order of mm2 with the increase in the transfer repetitions, and the master carrier with a trouble of significant signal drop finally failed in signal recording. Given that situation, we inspected the outward appearance of the master carrier before and after used in the test, and found some slight change in the appearance of the master carrier with a trouble of signal drop.
In addition, we have analyzed the profile of the used master carrier, and, as a result, found some minor change in the profile of the master carrier before and after used in the magnetic transfer test. From these, we considered that the large pressure applied to the master carrier in intimately contacting it with the slave medium caused the deformation of the master carrier. Accordingly, we again tried the magnetic transfer under a reduced pressure, but failed to ensure the intimate contact condition between the master carrier and the slave medium and, as a result, we could not realize uniform signal recording on the slave medium. Specifically, this suggests the presence of a factor that may augment the carrier deformation in addition to the pressure to be applied to the carrier in intimately contacting it with a recording medium. We carried out the same test in which the thickness of the master carrier was reduced to thereby lower the macromechanical bending toughness thereof, and found that the contact pressure necessary for ensuring the uniform intimate contact between the master carrier and the recording medium did not differ so much between the thick master carrier and the thin master carrier.